368 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



On the upper surface, and especially round the upper part of the 

 lateral surface, or round the margin of the very flattened specimens, 

 are the apertures of poriferous pits. The apertures are 2-5 mm. in 

 diameter, each surrounded by a fringe of projecting spicules, which 

 is sometimes thick and close and 3 mm. in length; fringe often more 

 or less worn down. The pits have no constant arrangement, al- 

 though there is sometimes a central one ; this is apical in a pyriform 

 young specimen 40 mm. in diameter. They usually number 8-12 on 

 a sponge. The pits are smooth walled and of the same elongated 

 ellipsoidal shape as in T. clavigera. The radial depth is 10-20 mm., 

 bottom width 7-9 mm. The wall in some is uniformly perforated 

 with thickly set minute pores leading into canals that abut against 

 the wall. But in the case of other pits apertures easily visible to the 

 eye, 1 mm. or thereabout in diameter, occur scattered over the gen- 

 eral poriferous surface. And in some cases the whole or a large part 

 of the pit wall is covered with apertures visible to the eye, ranging 

 down from 0.5 mm. in diameter to small pores. No other apertures 

 than those of the pits are found on the surface of the sponge, and it 

 would seem therefore that some of the pits must be afferent, others 

 efferent. 



The pits contain a great deal of shelly debris, and usually com- 

 mensal ophiuroids. Projecting obliquely from the wall are small 

 (trichodal) protriaenes; rhabdome about 2 \i thick, clads 12-20 pi 

 long. 



The ectosome does not include a distinct fibrous stratum, although 

 in its deeper part are numerous fiber cells disposed tangentially in 

 isolated tracts. Its outer part is occupied by a dense crust, 350-600 

 \). thick, of tangentially disposed oxeas (pi. 48, fig. 5, a~b). In the 

 young specimen referred to above this crust is only 150-250 y. thick. 

 Brownish granular cells are scattered in the dermal layer and 

 through the choanosome. The sponge is firm; often rather porous 

 owing to the number of small canals, 1-2 mm. in diameter. Some 

 specimens are more compact. Color brown, often dark. 



Strong skeletal bundles extend radially from the center of the 

 sponge to the surface, there expanding in the usual wa} r . There are 

 no radial ectosomal brushes of smaller megascleres. The radial 

 bundles include abundant oxeas, protriaene forms, and some 

 anatriaenes. Fringes of the poriferous pits include oxeas, pro- 

 triaenes, and prodiaenes. The root spicules include protriaenes and 

 very many anatriaenes. 



Spicules (pi. 48, fig. 5). — 1. Oxeas. Large equiended spicules, 7-9 

 mm. by 60-90 n, along with smaller ones, are abundant in the radial 

 bundles, sometimes projecting. In the specimen from station 5134 

 the radial oxeas of the under surface reach a length of 11 mm. 

 Similar oxeas, ranging from 1 mm. by 20 pi to less than half that 



